Front-to-back bonding with through-substrate via (tsv)

ABSTRACT

Methods for forming a semiconductor device structure are provided. The method includes providing a first semiconductor wafer and a second semiconductor wafer. A first transistor is formed in a front-side of the first semiconductor wafer, and no devices are formed in the second semiconductor wafer. The method further includes bonding the front-side of the first semiconductor wafer to a backside of the second semiconductor wafer and thinning a front-side of the second semiconductor wafer. After thinning the second semiconductor wafer, a second transistor is formed in the front-side of the second semiconductor wafer. At least one first through substrate via (TSV) is formed in the second semiconductor wafer, and the first TSV directly contacts a conductive feature of the first semiconductor wafer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the following co-pending and commonlyassigned patent applications: U.S. application Ser. No. 13/943,224,filed on Jul. 16, 2013 and entitled “Hybrid bonding with throughsubstrate via (TSV)”, and U.S. application Ser. No. 13/943,245, filed onJul. 16, 2013 and entitled “Mechanisms for forming three-dimensionalintegrated circuit (3DIC) stacking structure”, and U.S. application Ser.No. 13/943,401, filed on Jul. 16, 2013 and entitled “Hybrid bonding withthrough substrate via (TSV)”, and U.S. application Ser. No. 14/488,017,filed on Sep. 16, 2014 and entitled “Hybrid bonding with throughsubstrate via (TSV), and U.S. application Ser. No. 14/752,342, filed onJun. 26, 2015 and entitled “Method for forming hybrid bonding withthrough substrate via (TSV)”. This application is a Divisionalapplication of co-pending U.S. patent application Ser. No. 13/943,157,filed on Jul. 16, 2013, the entire contents of which is herebyincorporated by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductive layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon. Many integratedcircuits are typically manufactured on a single semiconductor wafer, andindividual dies on the wafer are singulated by sawing between theintegrated circuits along a scribe line. The individual dies aretypically packaged separately, in multi-chip modules, or in other typesof packaging, for example.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. These smallerelectronic components also require smaller packages that utilize lessarea than packages of the past, in some applications.

Three dimensional integrated circuits (3DICs) are a recent developmentin semiconductor packaging in which multiple semiconductor dies arestacked upon one another, such as package-on-package (PoP) andsystem-in-package (SiP) packaging techniques. Some 3DICs are prepared byplacing dies over dies on a semiconductor wafer level. 3DICs provideimproved integration density and other advantages, such as faster speedsand higher bandwidth, because of the decreased length of interconnectsbetween the stacked dies, as examples. However, there are manychallenges related to 3DICs.

BRIEF DESCRIPTION OF THE DRAWING

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1A-1F show cross-sectional representations of various stages offorming a semiconductor device, in accordance with some embodiments ofthe disclosure.

FIGS. 2A-2C show cross-sectional representations of various stages offorming a semiconductor device, in accordance with some embodiments ofthe disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description may include embodiments in which thefirst and second features are formed in direct or indirectly contact.

Embodiments of the disclosure provide mechanisms of forming asemiconductor device. FIGS. 1A-1F show cross-sectional representationsof various stages of forming a semiconductor device in accordance withsome embodiments of the disclosure. Referring to FIG. 1A, across-sectional representation of a portion of a semiconductor wafer 100and a portion of another semiconductor wafer 200 are shown in accordancewith some embodiments.

Semiconductor wafer 100 includes a semiconductor substrate 104, which ismade of silicon or other semiconductor materials and has a top surface104 a and a bottom surface 104 b. Alternatively or additionally,semiconductor substrate 104 may include other elementary semiconductormaterials such as germanium. In some embodiments, semiconductorsubstrate 104 is made of a compound semiconductor, such as siliconcarbide, gallium arsenic, indium arsenide, or indium phosphide. In someembodiments, semiconductor substrate 104 is made of an alloysemiconductor such as silicon germanium, silicon germanium carbide,gallium arsenic phosphide, or gallium indium phosphide. In someembodiments, semiconductor substrate 104 includes an epitaxial layer.For example, semiconductor substrate 104 has an epitaxial layeroverlying a bulk semiconductor.

Referring to FIG. 1A, device regions 103 are formed in a front-side 100a of semiconductor wafer 100 in a front-end-of-line (FEOL) process insome embodiments. Each device regions 103 includes a gate structure 109embedded in a dielectric layer 107, source/drain regions 110, andisolation structures 112, such as shallow trench isolation (STI)structures. Gate structure 109 includes a gate dielectric layer 106, agate electrode 108, and spacers (not shown). Device regions 103 shown inFIG. 1 are merely an example, and other devices may be formed in deviceregions 103.

Device regions 103 may form various N-type metal-oxide semiconductor(NMOS) and/or P-type metal-oxide semiconductor (PMOS) devices, such astransistors or memories, and the like, interconnected to perform one ormore functions. Other devices, such as capacitors, resistors, diodes,photo-diodes, fuses, and the like may also be formed in substrate 104.The functions of the devices may include memory, processing, sensors,amplifiers, power distribution, input/output circuitry, or the like. Insome embodiments, device regions 103 include N-type metal-oxidesemiconductor (NMOS) and/or P-type metal-oxide semiconductor (PMOS)transistors.

A metallization structure 122 is formed over substrate 104, e.g., overdevice regions 103. In some embodiments, metallization structure 122includes interconnect structure, such as a contact plug 114 andconductive features 124. Conductive features 124 are embedded in aninsulating material 126. Metallization structure 122 is formed in aback-end-of-line (BEOL) process in some embodiments. In someembodiments, contact plug 114 is made of conductive materials, such ascopper, copper alloy, aluminum, alloys or combinations thereof.Conductive features 124 are also made of conductive materials.Alternatively, other applicable materials may be used. In someembodiments, contact plug 114 and conductive features 124 are made ofconductive materials which are heat resistant, such as tungsten (W), Cu,Al, or AlCu. In some embodiments, insulating material 126 is made ofsilicon oxide. In some embodiments, insulating material 126 includesmultiple dielectric layers of dielectric materials. One or more of themultiple dielectric layers are made of low dielectric constant (low-k)materials. In some embodiments, a top dielectric layer of the multipledielectric layers is made of SiO₂. Metallization structure 122 shown ismerely for illustrative purposes. Metallization structure 122 mayinclude other configurations and may include one or more conductivelines and via layers.

A bonding layer 142, which is a dielectric layer, is formed over thefront-side 100 a of semiconductor wafer 100, e.g. on metallizationstructure 122. In some embodiments, bonding layer 142 is made of asilicon-containing dielectric, such as silicon oxide, silicon oxynitrideor silane oxide.

In some embodiments, bonding layer 142 is formed by plasma enhancedchemical vapor deposition (PECVD). In some other embodiments, bondinglayer 142 is formed by a spin-on method. In some embodiments, bondinglayer 142 has a thickness in a range from about 5 nm to about 300 nm.

As shown in FIG. 1A, devices, such as transistor including gatestructure 109, are formed in front-side 100 a of semiconductor wafer100, while no devices are formed in a backside 100 b of semiconductorwafer 100.

Semiconductor wafer 200 includes a substrate 204, which is similar tosubstrate 104. Substrate 204 has a top surface 204 a and a bottomsurface 204 b. A bonding layer 242, which is a dielectric layer, isformed over a backside 200 b of semiconductor wafer 200, e.g. on bottomsurface 204 b of substrate 204. In some embodiments, bonding layer 242is similar to bonding layer 142. No devices are pre-formed insemiconductor wafer 200.

As shown in FIG. 1A, substrate 204 has a height H₁ from top surface 204a to bottom surface 204 b in a range from about 50 μm to about 775 μm.

Before semiconductor wafers 100 and 200 are bonded together, two bondinglayers 142 and 242 are treated. Bonding layers 142 and 242 are treatedby a dry treatment or a wet treatment. The dry treatment includes aplasma treatment. The plasma treatment is performed in an inertenvironment, such as an environment filled with inert gas including N₂,Ar, He or combinations thereof. Alternatively, other types of treatmentsmay be used. In some embodiments, both of bonding layers 142 and 242 aremade of silicon oxide, and a plasma process is performed to bondinglayers 142 and 242 to form Si—OH bonds on the surface of bonding layers142 and 242 prior to bonding.

Referring to FIG. 1B, after the alignment is performed, semiconductorwafer 100 is boned to semiconductor wafer 200 to form a 3DIC stackingstructure 300. As shown in FIG. 1B, when semiconductor wafer 200 isbonded to semiconductor wafer 100, bottom surface 204 b of substrate 204faces top surface 104 a of substrate 104, and bonding layer 142 isbonded to bonding layer 242. Bonding of semiconductor wafers 100 and 200is performed under pressure and heat. In some embodiments, the pressurefor bonding is in a range from about 0.7 bar to about 10 bar. In someembodiments, the heat applied to semiconductor wafers 100 and 200includes an anneal operation at a temperature in a range from about 20°C. to about 1000° C. . The bonding process may be performed in an N₂environment, an Ar environment, an He environment, an inert-mixing gasenvironment, or combinations thereof.

As shown in FIG. 1B, stacking structure 300 includes a bonding structure150. Bonding structure 150 includes bonding layers 142 and 242 bondedtogether. Therefore, backside 200 b of semiconductor wafer 200 is bondedto front-side 100 a of semiconductor wafer 100. If some devices areformed in semiconductor wafer 200 before bonding, semiconductor wafers100 and 200 have to be precisely aligned before bonding. In contrast,since no devices are pre-formed in semiconductor wafer 200, an aligningprocess is not required for bonding of semiconductor wafers 100 and 200.

After bonding semiconductor wafers 100 and 200, a thinning process 11 isperformed on top surface 204 a of semiconductor wafer 200, referring toFIG. 1C. Thinning process 11 may include a grinding operation and apolishing operation (such as chemical mechanical polishing (CMP)). Afterthinning process 11, a wet etching operation is performed to remove thedefects formed on top surface 204 a of semiconductor wafer 200. Afterthinning process 11, substrate 204 has a height H₂ from top surface 204a ′ to bottom surface 204 b of semiconductor substrate 204 in a rangefrom about 0.2 μm to about 10 μm. Height H₂ is smaller than height H₁.In some embodiments, and a ratio of height H₂ to H₁ is in a range fromabout 0.0002 to about 0.99.

After thinning semiconductor wafer 200, device regions 203 are formed infront-side 200 a of semiconductor wafer 200, referring to FIG. 1D.Device regions 203 are formed in a front-end-of-line (FEOL) process insome embodiments. Each device regions 203 includes a gate structure 209embedded in a dielectric layer 207, source/drain regions 210, andisolation structures 212, such as shallow trench isolation (STI)structures. Gate structure 209 includes a gate dielectric layer 206, agate electrode 208, and spacers (not shown). A contact plug 214 isformed over device regions 203, e.g. on gate structure 209. In someembodiments, formations of device regions 203 and contact plug 214 areperformed under a relatively low temperature, such that metallizationstructure 122 will not be damaged during the processes. However, in someembodiments, metallization structure 122, including contact plug 114 andconductive features 124, are made of heat resistant conductivematerials, and thus formations and materials of device regions 203 andcontact plug 214 can be similar to those of device regions 103 andcontact plug 114. In some embodiments, device regions 203 include NMOSand/or PMOS transistors.

As shown in FIG. 1D, devices, such as transistors including gatestructure 209, are formed in front-side 200 a of semiconductor wafer200, while no devices are formed in backside 200 b of semiconductorwafer 200. In addition, backside 200 b of semiconductor wafer 200 isbonded to front side 100 a of semiconductor wafer 100, and therefore theresulting stacking structure 300 is a front-to-back (face-to-back)stacking structure.

After device regions 203 are formed, through-substrate via (TSV) 400 isformed through second semiconductor wafer 200, referring to FIG. 1E.Through-substrate via (TSV) 400 is used to provide electricalconnections and for heat dissipation for 3DIC stacking structure 300.Although FIG. 1E only shows one TSV, more than one TSV may be formed topass through second semiconductor wafer 200.

TSV 400 includes a liner 410, a diffusion barrier layer 420, and aconductive material 430. TSV 400 is formed by the following operations.Firstly, a TSV opening is formed extending to conductive feature 124 aof semiconductor wafer 100 by one or more etching processes. After theTSV opening is formed, liner 410 is formed on sidewalls of the TSVopening to act as an isolation layer, such that conductive materials ofTSV 400 and semiconductor substrate 204 do not directly contact witheach other. Afterwards, diffusion barrier layer 420 is conformallyformed on liner 410 and on the bottom of the TSV opening. Diffusionbarrier layer 420 is used to prevent conductive material 430, which willbe formed later, from migrating to device regions 103 and 203. Afterdiffusion barrier layer 420 is formed, conductive material 430 is usedto fill into the TSV opening. Afterwards, excess liner 410, diffusionbarrier layer 420, and conductive material 430, which are on the outsideof the TSV opening, are removed by a planarization process, such as achemical mechanical polishing (CMP) process, although any suitableremoval process may be used.

Liner 410 is made of an insulating material, such as oxides or nitrides.Liner 410 may be formed by using a plasma enhanced chemical vapordeposition (PECVD) process or other applicable processes. Liner 410 maybe a single layer or multi-layers. In some embodiments, liner 410 has athickness in a range from about 100 Å to about 5000 Å.

In some embodiments, diffusion barrier layer 420 is made of Ta, TaN, Ti,TiN or CoW. In some embodiments, diffusion barrier layer 420 is formedby a physically vapor deposition (PVD) process. In some embodiments,diffusion barrier layer 420 is formed by plating. In some embodiments,conductive material 430 is made of copper, copper alloy, aluminum,aluminum alloys, or combinations thereof. Alternatively, otherapplicable materials may be used.

As shown in FIG. 1E, in some embodiments, TSV 400 has a width W₁ in arange from 0.025 μm to about 4 μm. In some embodiments, TSV 400 has adepth D₁ in a range from 0.2 μm to about 10 μm. In some embodiments, TSV400 has an aspect ratio (D1/W1) in a range from 2 to about 15.

As shown in FIG. 1E, TSV 400 is used to connect conductive features 124a on semiconductor wafer 100 to second semiconductor wafer 200. If a TSVsimilar to TSV 400 is formed in semiconductor wafer 200 with a height H₁as shown in FIG.1B, the TSV will have a higher aspect ratio than TSV400. With high aspect ratio, filling materials into the TSV openingbecomes challenging. Voids may form in the TSV opening. In addition, dueto insufficient sidewall coverage of liner 410 or diffusion barrierlayer 420, some extrusion or diffusion problems related to conductivevia material 430 may occur. In contrast, as shown in FIG. 1E, since theheight of semiconductor wafer 200 is reduced from H₁ to H₂, TSV 400 hasa relative smaller aspect ratio. Therefore, the void problems and theextrusion or diffusion problems resulting from a high aspect ratio ofthe TSV are resolved or greatly reduced. In addition, the overallpackage height of 3DIC stacking structure 300 is reduced to meetadvanced packaging requirements. Therefore, 3DIC stacking structure 300achieves small form factor.

In addition, devices in the vicinity of the TSV suffer from seriousperformance degradation due to the stress induced by the TSV. A keep-outzone (KOZ) is used to define a region where no devices could be placedwithin. In some embodiments, keep-out zone (KOZ) is defined by adistance W₂, which is measured from a sidewall 400 a of TSV 400 to anearest gate structure 209. Since semiconductor wafer 200 has arelatively small height H₂ due to thinning, the depth D₁ of TSV 400 ismade smaller, resulting in a smaller width W₁. Therefore, overall stressinduced by TSV 400 is reduced, and distance W₂ is also made smaller inFIG. 1E. In some embodiments, distance W₂ is in a range from about 0.01μm to about 3 μm. When distance W₂ is smaller, a larger area of deviceregions 203 may be used. As a result, integrated intensity of devices indevice regions 203 is further improved.

After TSV 400 is formed, an interconnect structure 500 is formed onfront-side 200 a of second semiconductor wafer 200, referring to FIG.1F. Interconnect structure 500 is electrically connected to conductivefeatures 124 a of semiconductor wafer 100 via TSV 400. Interconnectstructure 500 includes conductive features 510, such as conductivelines, vias, or conductive pads, formed in an insulating material 520.The metal routings of the conductive features shown in FIG. 1F, aremerely examples. Alternatively, other designs of metal routings ofconductive features may be used according to actual application.

As shown in FIG. 1F, in stacking structure 300, devices, such astransistors indlucing gate structure 109, are formed in fornt-side 100 aof semiconductor wafer 100 while no devices are formed in backside 100 bof semiconductor wafer 100. Devices, such as transistors including gatestructure 209, are formed in fornt-side 200 a of semiconductor wafer 200while no devices are formed in backside 200 b of semiconductor wafer200. Backside 200 b of semiconductor wafer 200 is bonded to front-side100 a of semiconductor wafer 100, and therefore stacking structure 300is a front-to-back structure. In addition, interconnect structure 500 isformed on front-side 200 a of semiconductor wafer 200, and TSV 400directly contacts interconnect structure 500 and conductive feature 124a of semiconductor wafer 100.

If devices are pre-formed on semiconductor wafer 200 before bonding tosemiconductor wafer 100, semiconductor wafer 200 cannot be thinned sincethe devices are located on front-side 200 a of semiconductor wafer 200.Therefore, it will be difficult to form a small TSV. In contrast, nodevices are pre-formed on semiconductor wafer 200, and thereforesemiconductor wafer 200 can be thinned from top surface 204 a ofsubstrate 204. After thinning process 11, the devices, such astransistors including gate structure 209, and TSV 400 could besubsequently formed in front-side 200 a of semiconductor wafer 200.Therefore, a relatively small TSV 400 is formed in front-to-back 3DICstacking structure 300.

In addition, other processes may also be performed to 3DIC stackingstructure 300, and 3DIC stacking structure 300 may be diced to formindividual chips afterwards.

FIGS. 2A-2C show cross-sectional representations of various stages offorming a semiconductor device, in accordance with some embodiments ofthe disclosure. As shown in FIG. 2A, the 3D stacking structure 300′ inFIG. 2A is almost the same with 3D stacking structure 300 except anadditional TSV 400 b is formed in semiconductor wafer 200. The formationof stacking structure 300′ may involve additional patterning and etchingprocesses. For example, a first TSV opening is formed throughsemiconductor wafer 200 to expose a portion of a conductive feature 124a of semiconductor wafer 100. After the first TSV opening is formed, asecond TSV opening is formed through semiconductor wafer 200 to extendover device regions 103 of semiconductor wafer 100. Afterwards, liners410 b and 410, diffusion barrier layers 420 b and 420, and conductivematerials 430 b and 430 are used to fill in the first and second TSVopenings to form TSVs 400 b and 400. As shown in FIG. 2A, TSV 400 bincludes liner 410 b similar to liner 410, diffusion barrier layer 420 bsimilar to diffusion layer 420, and conductive material 430 b similar toconductive material 430, but TSV 400 b further extends to a region inbackside 100 b of semiconductor wafer 100.

In some embodiments, TSV 400 b has a width W₃ in a range from about 0.3μm to about 10 μm. In some embodiments, TSV 400 b has a depth D₂ in arange from about 15 μm to about 100 μm. In some embodiments, TSV 400 bhas an aspect ratio (D₂/W₃) in a range from about 5 to about 15. A ratioof depth D₂ to depth D₁ is in a range from about 2 to about 15.

Referring to FIG. 2B, interconnect structure 500 is formed on front-side200 a of semiconductor wafer 200. Interconnect structure 500 includesconductive features, such as conductive lines, vias, or conductive pads,formed in an insulating material. The metal routings of the conductivefeatures shown in FIG. 2B, are merely an example. Alternatively, otherdesigns of metal routings of conductive features may be used accordingto actual application. In some embodiments, substrate 104 has a heightH₃ in a range from about 10 μm to about 100 μm.

After forming interconnect structure 500, semiconductor wafer 100 isthinned from bottom surface 104 b of substrate 104 to expose a bottom ofTSV 400 b, referring to FIG. 2C. After the thinning process,redistribution (RDL) structure 160 is formed on backside 100 b ofsemiconductor wafer 100 (e.g. thinned bottom surface 104 b′ of substrate104). RDL structure 160 includes a metal pad 162 formed in a passivationlayer 164. Metal pad 162 is electrically connected to exposed TSV 400 b.In some embodiments, metal pad 162 is made of conductive materials withlow resistivity, such as copper (Cu), aluminum (Al), Cu alloys, Alalloys, or other applicable materials. Although FIG. 2C only shows oneRDL structure 160, more than one RDL structures may be formed.

An under bump metallization (UBM) layer 165 is formed on metal pad 162,and a conductive element 166 (such as solder ball) is formed over UBMlayer 165. UBM layer 165 may contain an adhesion layer and/or a wettinglayer. In some embodiments, UBM layer 165 is made of titanium (Ti),titanium nitride (TiN), tantalum nitride (TaN), tantalum (Ta), or thelike. In some embodiments, UBM layer 165 further includes a copper seedlayer. In some embodiments, conductive element 166 is made of conductivematerials having low resistivity, such as solder or solder alloy.Exemplary elements included in the solder alloy may include Sn, Pb, Ag,Cu, Ni, Bi, or combinations thereof

In some embodiments, interconnect structure 500 is electricallyconnected to another package (not shown) on the backside 100 b ofsemiconductor wafer 100 via TSV 400 b, RDL structure 160 and conductiveelement 166. In some embodiments, additional conductive structures, suchas additional RDL structures, are formed over interconnect structure500, such that semiconductor wafers 100 and 200 can be connected toother package substrates (not shown).

As shown in FIG. 2C, TSVs 400 and 400 b individually provide differentfunctions. TSV 400 directly contacts interconnect structure 500 andconductive feature 124 a, and TSV 400 b directly contacts interconnectstructure 500 and RDL structure 160. Therefore, semiconductor wafer 200is electrically connected to semiconductor wafer 100 via TSV 400, andsemiconductor wafer 200 is electrically connected to another packagestructure (not shown) via interconnect structure 500 and TSV 400 b. TSVs400 and 400 b provide a fast conductive path to connect semiconductorwafer 100, semiconductor wafer 200, and/or other package structures,without the formation of complicated metal routings.

Embodiments of mechanisms for forming a semiconductor device areprovided. A backside of a second semiconductor is bonded to a front-sideof a first semiconductor, which has devices, such as transistors, formedtherein. After the second semiconductor wafer is bonded to the firstsemiconductor wafer, the front-side of the second semiconductor waferwithout devices pre-formed therein is thinned. After the thinningprocess, devices, such as transistors, are formed in the front-side ofthe second semiconductor wafer to form a front-to-back (face-to-back)stacking structure. A relatively small TSV is formed in thefront-to-back stacking structure. Alternatively, TSVs having differentsizes are formed in the front-to-back stacking structure.

In some embodiments, a method for forming a semiconductor devicestructure is provided. The method includes providing a firstsemiconductor wafer and a second semiconductor wafer. A first transistoris formed in a front-side of the first semiconductor wafer, and nodevices are formed in the second semiconductor wafer. The method furtherincludes bonding the front-side of the first semiconductor wafer to abackside of the second semiconductor wafer and thinning a front-side ofthe second semiconductor wafer. After thinning the second semiconductorwafer, a second transistor is formed in the front-side of the secondsemiconductor wafer. At least one first through substrate via (TSV) isformed in the second semiconductor wafer, and the first TSV directlycontacts a conductive feature of the first semiconductor wafer.

In some embodiments, a method for forming a semiconductor devicestructure is provided. The method includes providing a firstsemiconductor wafer and a second semiconductor wafer, and no devices areformed in the second semiconductor wafer. The method includes bondingthe front-side of the first semiconductor wafer to a backside of thesecond semiconductor wafer by a bonding layer, and the bonding layer isformed between the first semiconductor wafer and the secondsemiconductor wafer. The method also includes thinning a front-side ofthe second semiconductor wafer and forming a second transistor in thefront-side of the second semiconductor wafer. The method furtherincludes forming at least one first TSV in the second semiconductorwafer, and the first TSV passes through the bonding layer. The methodincludes forming at least one second TSV in the second semiconductorwafer and the first semiconductor wafer and thinning a backside of thefirst semiconductor wafer to expose the second TSV.

In some embodiments, a method for forming a semiconductor devicestructure is provided. The method includes providing a firstsemiconductor wafer and a second semiconductor wafer. A first bondinglayer is formed over a front-side of the first semiconductor wafer, anda second bonding layer is formed over a backside of the secondsemiconductor wafer. The method includes bonding the first semiconductorwafer and the second semiconductor wafer via bonding the first bondinglayer and the second bonding layer. The method also includes thinning afront-side of the second semiconductor wafer and forming a secondtransistor in the front-side of the second semiconductor wafer. Themethod also includes forming at least one first TSV in the secondsemiconductor wafer, and the first TSV passes through the bonding layer.The method further includes forming at least one second TSV in thesecond semiconductor wafer and the first semiconductor wafer and formingan interconnect structure over the front-side of the secondsemiconductor wafer.

Although embodiments of the present disclosure and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. For example, it will be readily understood by those skilled inthe art that many of the features, functions, processes, and materialsdescribed herein may be varied while remaining within the scope of thepresent disclosure. Moreover, the scope of the present application isnot intended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present disclosure,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present disclosure. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method for forming a semiconductor devicestructure, comprising: providing a first semiconductor wafer and asecond semiconductor wafer, wherein a first transistor is formed in afront-side of the first semiconductor wafer, and no devices are formedin the second semiconductor wafer; bonding the front-side of the firstsemiconductor wafer to a backside of the second semiconductor wafer;thinning a front-side of the second semiconductor wafer; forming asecond transistor in the front-side of the second semiconductor wafer;and forming at least one first TSV in the second semiconductor wafer,wherein the first TSV directly contacts a conductive feature of thefirst semiconductor wafer.
 2. The method as claimed in claim 1, furthercomprising: forming at least one second TSV in the first semiconductorwafer and the second semiconductor wafer to directly contact aredistribution (RDL) structure formed over a backside of the firstsemiconductor wafer.
 3. The method as claimed in claim 2, wherein thesecond TSV has a second height larger than a first height of the firstTSV.
 4. The method as claimed in claim 2, wherein the interconnectstructure is electrically connected to a package substrate over thebackside of the second semiconductor wafer through the second TSV. 5.The method as claimed in claim 1, further comprising: forming aninterconnect structure over the front-side of the second semiconductorwafer, wherein the interconnect structure is electrically connected tothe conductive feature of the first semiconductor wafer through thefirst TSV.
 6. The method as claimed in claim 1, wherein bonding thefront-side of the first semiconductor wafer to the backside of thesecond semiconductor wafer is by a bonding layer, and the bonding layeris formed between the first semiconductor wafer and the secondsemiconductor wafer.
 7. The method as claimed in claim 6, wherein thefirst TSV passes through the bonding layer.
 8. The method as claimed inclaim 1, wherein forming at least one first TSV in the secondsemiconductor wafer comprises: forming a first TSV opening in the secondsemiconductor wafer; forming a liner on sidewalls of the first TSVopening; forming a diffusion barrier layer on the liner and the bottomof the first TSV opening; and forming a conductive material on thediffusion barrier layer.
 9. A method for forming a semiconductor devicestructure, comprising: providing a first semiconductor wafer and asecond semiconductor wafer, wherein no devices are formed in the secondsemiconductor wafer; bonding the front-side of the first semiconductorwafer to a backside of the second semiconductor wafer by a bondinglayer, wherein the bonding layer is formed between the firstsemiconductor wafer and the second semiconductor wafer; thinning afront-side of the second semiconductor wafer; forming a secondtransistor in the front-side of the second semiconductor wafer; andforming at least one first TSV in the second semiconductor wafer,wherein the first TSV passes through the bonding layer; and forming atleast one second TSV in the second semiconductor wafer and the firstsemiconductor wafer; and thinning a backside of the first semiconductorwafer to expose the second TSV.
 10. The method as claimed in claim 9,before thinning the backside of the first semiconductor wafer, furthercomprising: forming an interconnect structure over the front-side of thesecond semiconductor wafer, wherein the interconnect structure iselectrically connected to a conductive feature of the firstsemiconductor wafer through the first TSV.
 11. The method as claimed inclaim 9, wherein the interconnect structure comprises a first conductiveline and a second conductive line, the first conductive line has a firstsurface facing a top surface of the first TSV, and no via is formed onthe first surface.
 12. The method as claimed in claim 9, furthercomprising: forming a first redistribution (RDL) structure on a backsideof the first semiconductor wafer, wherein the second TSV contacts withthe first RDL structure.
 13. The method as claimed in claim 12, whereinforming the first RDL structure comprises: forming a metal pad on abottom surface of the second TSV; forming an under bump metallization(UBM) layer on the metal pad; and forming a conductive element on theUBM layer.
 14. The method as claimed in claim 9, wherein a firsttransistor is formed over the front-side of the first semiconductorwafer, and a conductive feature is formed over the first transistor, andthe first TSV contacts with the conductive feature.
 15. A method forforming a semiconductor device structure, comprising: providing a firstsemiconductor wafer and a second semiconductor wafer, wherein a firstbonding layer is formed over a front-side of the first semiconductorwafer, and a second bonding layer is formed over a backside of thesecond semiconductor wafer; bonding the first semiconductor wafer andthe second semiconductor wafer via bonding the first bonding layer andthe second bonding layer; thinning a front-side of the secondsemiconductor wafer; forming a second transistor in the front-side ofthe second semiconductor wafer; and forming at least one first TSV inthe second semiconductor wafer, wherein the first TSV passes through thebonding layer; and forming at least one second TSV in the secondsemiconductor wafer and the first semiconductor wafer; and forming aninterconnect structure over the front-side of the second semiconductorwafer.
 16. The method as claimed in claim 15, further comprising:thinning a backside of the first semiconductor wafer to expose thesecond TSV; and forming a first redistribution (RDL) structure on abackside of the first semiconductor wafer, wherein the second TSVdirectly contacts with the interconnect structure and the first RDLstructure.
 17. The method as claimed in claim 15, wherein the firstbonding layer and the second bonding layer respectively made of siliconoxide, silicon oxynitride or silane oxide.
 18. The method as claimed inclaim 15, wherein the first TSV as a first depth, the second TSV has asecond depth larger than the first depth.
 19. The method as claimed inclaim 15, wherein a first transistor is formed over the front-side ofthe first semiconductor wafer, and a conductive feature is formed overthe first transistor, and the first TSV contacts with the conductivefeature.
 20. The method as claimed in claim 15, wherein the interconnectstructure comprises a first conductive line and a second conductiveline, the first conductive line has a first surface facing a top surfaceof the first TSV, and no via is formed on the first surface.